Traffic control system



3 R. c. HITCHCOCK 2,094,598

TRAFFIC CONTROL SYSTEM Filed Dec. 27. 1930 2 Sheets-Sheet 1 WITNESSES; INVENTOR RichardCf/izchcock.

ATTORNE Oct. 5, 1937. c, rrc c c w 2,094,598

TRAFFI CONTROL SYSTEM mmardam'zchcoc/c.

. BY \7L Patented Oct. 5, 1937 PATENT OFFICE} 2,094,598 TRAFFIC :CQNTROL SYSTEM Richard C. 'Hitchc0ck,'Wilkinsburg, Pa, assignor to Westinghouse "Electric & Manufacturing Company, a corporation of Pennsylvania Application December 27, 1930,-Serial No. 505,071 4 Claims. 01. 177-337.)

My invention relates to traffic-control systems and has particular relation to photo-sensitive automatic-traific control systems.

.Automatic-traflic-control systems are ordinarily .5 ,providedfor:regulatingthe right-of-way at'an intersection of a plurality of thoroughfares. Although they "in general apply to intersections of any type they are more urgently needed at'an intersection :of major and minor thoroughfares (110 than .at intersections where all of the .thoroughfares are major; 7

-At a major-minor intersection the traffic signalling is so adjusted that in the absence of vehicles along the minor thoroughfare, the rightof-way signal is given to the major thoroughfare, and the signalling system remains -*in this condition as longas-thereis no traffic along the ,minor thoroughfare. However, after apredetermined period after a vehicle moving towards the 1 intersection along the minor highway appears at .the intersection, the signalling system is -:motivated and the right-of-way signal is given to the minor highway.

To simplify the structure of the system it is desirable that the element, whereby .the change in .thesignallingsystem-is'produced, and which shall hereinafter be designated as a street device, he so disposed that it comes under the influence of all vehicles passing between the longitudinal boundaries .of the thoroughfare. That is to say, the street device .comes under .the :influence of vehicles moving away from the intersection as 'well .as vehicles moving up to the intersection. This .feature of the system introduces-the problem of providing a device whereby the system is .not

:operated by vehicles that under ordinary circumstances .have .no necessity of operating it; that is, vehicles moving away :from the intersection.

.In experimenting with trafiic control systems,

.I have :found that the :provisionof such a device is .notiat all a simple matter. Relays of -the pendulum type are most commonly rutilized in this connection in equipment constructed as dictated by the teachings .of the ,prior art;,-with which I am familiar. ,Howevenzmy experiments have indicated that relays of this type cause consider- .able interference troubles in the radio-receiving equipment gr people living in the neighborhood of the intersection where the system is installed. The :relays of the dash-pot type and relays of the thermostat type of which I am aware are .unstable .and (unreliable in the present I connection, and require considerable servicing.

3155; is acoordinglyanobject oivmy invention to provide apparatus 'for introducing .a time delay in the action of "a street device in an automatic traffic control system, that .shall be stable and reliable.

Another object of my invention is togprovide a .5 continuance for producing a-time-delay in the action of a street device in a trafiic control (system that shall not produce a radio interference. A further object of :myinvention is toprovide a simple and inexpensive time+de1ayelement7for 10 an automatic trafiic control system.

A still further object of my invention is to provide an automatic trafiic control system wherein a device is introduced whereby a-timedelay of :predetermined length in (the action of 15 "the street device is attained.

:An ancillary object of my invention is to pro- *Vide an automatic traffic control system wherein the duration of the signals along the highways is regulated by trafiic traversing the highways. 20

'A further ancillary object of my invention is to provide .a traflic system .for a-ma-jor-minor of predetermined length after it is excited by a vehicle, and wherein'the length of the signal is regulated by the density of the traffic; 35

According to my invention I provide an "automatic traffic control system wherein thetimedelay in the ultimate action of the street device is effected by the coaction of a plurality of sectors rotated by a motor. One of the sectors may 40 be utilized to initiate the action of the traific signal system, in response'to the disturbance of a street device, while another sector is utilized to time the action. In addition to the time delay motor the system is, of course, also equlppedwith A5 a motor that drives a program controller, which,

in turn, regulates the periodicity of the traffic. To accurately time the delay produced, the

sectors of the time delay contrivance are driven through a synchronous motor which-may :be Lin- 50 stantly stopped by the application of a direct current to its windings. The motor is .so .connectedin the-circuit of thesystem-that the direct current is applied after a predetermined interval :of time and the motor stops in such a position that the sectors occupy their original positions.

Finally, the system is made responsive to the density of the traffic along the thoroughfares by connecting the motor, through which the program controller is driven, in an electrical circuit similar to the circuit of the delay motor, discussed hereinabove. The motor in this case is also synchronous and responds to the application of direct current by stopping. The direct current is applied when the street device comes under the instantaneous influence of a vehicle, simultane-v ous with the indication of a right-of-way signal for the thoroughfare where it is located, and along which the vehicle is moving.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments, when read in connection with the accompanying drawings, in which:

Figure 1 is a diagrammatic view showing the arrangement of the elements of a simple embodiment of my invention, and

Fig. 2 is a diagrammatic View showing the arrangement of the elements of a more complex embodiment of my invention.

In Fig. 1 the intersection I of a major highway 3 and a minor highway is illustrated. A system of trafiic signals i is situated at a convenient point in the intersection of the highways 3 and 5 and, with no traffic along the minor highway 5, indicates a right-of-way signal for the major highway 3. Street devices, comprising a source of light 9 and a photo-sensitive element ll, influenced by the light from the source, are disposed along the minor highway 5 on each side of the intersection l.

Although other relative orientations of the source of light 9 and the photo-sensitive device H are possible, I have found that a preferable arrangement is attained by disposing the source 9 on one side l3 'of the thoroughfare, and the photo-sensitive device H on the opposite side 15 thereof.

The photo-sensitive device H is illustrated in the drawings with the conventional symbol of a photo-cell. However, the illustration should only be regarded as symbolical. The device may be a photo-cell. On the other hand, it is preferable that a system for amplifying the photo-cell current be supplied. This system may be simply an ordinary thermionic amplifier. However, I have found particularly useful in this connection an The current from the photo-sensitive devices ll passes through the exciting coil 11 of a relay l9 and energizes the relay under ordinary circumstances. The relay l 9 is in an energized condition when, as is illustrated in Fig. 1, no vehicles are present along the minor thoroughfare 5 in r the vicinity of the intersection l.

However, when a vehicle stops in such a position as to obstruct the light from the source 9 to the photo-sensitive element H, the relay l9, as-

sociated with the photo-sensitive device H is deenergized.

The relay l9 must remain in a deenergized condition until an initiating sector 2| rotated from a motor 23 comes into contact with a brush 25 connected to a lead 2'! which, in turn, is connected to one element of the fixed contact 29 of the relay l9. When the circuit to contact 29 is closed, a circuit is completed from one bus line 3| of the power supply source, through a lead 33, connecting the bus line 3! to the coil 35 of a second relay 31, the function of which will be described hereinafter, through the coil 35 of the relay 31, a further lead 39, the movable contactor 4| of the first relay E9, the lead 21, the initiating sector 2|, a branch lead 43, and the lead 45 to the remaining bus line 4'! of the power supply source.

The second relay 3i, to which reference was made above, is equipped with two normally open contactors 49 and 5| and one normally closed contactor 53. When the relay 3? is in a deenergized state a circuit is completed, from one power line 41, through the lead 95, the closed contactor 53,

'a second lead 55, a conducting segment 51, adapted to be rotated from the motor 59 which drives a program controller 5!, through a lead 63, the exciting coil 65 of athird relay 6?, a lead (59 and the remaining bus line 3! of the power source. It is seen that the third relay 5'4 is in an energized condition as long as the second relay 3'! is in a deenergized condition.

The third relay 5! is equipped with one contactor H, which is open when the relay 6! is energized and one contactor 13, which is closed when the relay 6'! is energized. The leads 15, TI, and 19 whereby power is supplied to the motor 59 which drives the program controller 5! are connected to the fixed contacts 8| of the open contactor H, while the leads 83, 85 and 81, whereby power is supplied to a braking device 89 for the motor 59, are connected through the fixed contacts 9| of the closed contactor 13.

It is seen, therefore, that when the relay 6'! is in an energized condition; (that is to say, when the light from the source 9 to the photo-sensitive device II is not obstructed) the program control motor 59 is not rotating. Furthermore, when the light from the source 9 is obstructed and the initiating segment 2| makes contact through the exciting coil 35 of the relay 31, the closed contactor 53 of the relay 3] is opened, but a second circuit is completed from one bus line 47 through the lead 45, the lead 43, connected to the central point 93 of the initiating sector 2!, the shaft 95, on which the initiating sector 2| is rotated, a timing sector 91, centrally disposed on the shaft 95 of the initiating sector 2| and rotated from the motor 23 that drives the initiating sector, a lead 99, a contactor 5! that has been closed by the excitation of the relay 31, the lead 55, the conducting segment 51, the lead 93, the exciting coil 65 of the relay 61, and the lead 69, to the bus line 3|, as was the case with the circuit described above.

It is seen that by the action of the vehicle on the street device the circuit, whereby the relay 5'! controlling the program control motor 59 is held in a state of excitation, has been transferred from a simple contactor 53' to a timing sector 91. The initiating sector 2! and the timing sector 9'! are so disposed on their driving shaft 95 that the brushes 25 and IM associated with them make contact simultaneously. However, since the contact of the initiating sector is only instantaneous a lock-in circuit is provided therefore, from a bus line 4-I, l of .the power supply source, through :thellead :45, :the remaining normally open contactor 49 of the relay 31, the lead 50, the nowclosedcontactor 41,.thelead 39, the :coil :01" the relay :3! :and-the remaining bus 'line 3l of the'source. The contactor M of relay I9 and the contactor 49 of :relay 3T1 are connect- :ed in :series relationship with the 0011 4350f relay T31 and, therefore, the lock-in is completely .broken if the relay :IS is re-energized :ashappens when the=vehicle moves away from the intersection J and no *longer obstructs the radiation to :the photo-cell.

The relay "61 remains in :an energized-condition :as long ;as the timing sector 9:1 is in contact with its associated brush :I lll. -When the brush it! and the timing sector 9] are disengaged, the relay .61 associated with the programcontrol motor 59, .is deenergized, the motor windings are energized and the program controller BI is rostated. The resultof the rotation :of the program controller BI is to :cause'the system ofsignals 1,

-=located .at the intersection, 'to go through the :customarycycle, indicating right-of-way for the minor highway after a predetermined time.

Simultaneously with the rotation of the program controller 161, the conducting segment '51 disposed on the same shaft I 03 as the :program controller is rotated and the circuit through the relay :6], associated with the program control motor :59, :is opened. As a result, it is possible for the lphoto-sensi'tive device II to become re- .energized, the :relay 19 -associatedtherewith to .be :re-excited, and the relay 3?! associated with the time-delay equipment to be deenergized without disturbing the cycle :of the trafiic signals.

ilvlore concisely stated, the system operates as follows:

.As soon as the vehicle obstructs the control 'light from 'lamp 9, relay il 9 closes contacts 29, andassoon as initiating sector S21 reaches'brush 25 and :brush 11)] :makes contact :with sector 91, current .fiows through bridging member 5I of relay 31 to brushes 105, even though relay '31 is stilllen'ergized and contacts 53 still open. Relay ii-I "remains closed and keeps the braking coil 89 energized. The, signals stand in their last mentioned condition as long as brush Ill! makes contact with sector 91. When these two break contact, braking coil 89 is deenergized provided relay 31 is still raised, this latter being the'case if a vehicle still interrupts the light beam from 9, deenergizing 'the braking coil 89, and simultaneously closing of motor circuit starts the program controller 'in rotation a second consecutive time.

It is well to point out that the system is reverted to its initial condition when the conduct- .ing segment 51 associated with-theprogram controller 61 engages its corresponding brushes 105. In this condition, the program control motor 59 is inactive, the right-of-way signal is .indicated for the main thoroughfare .3 while a stop signal is indicated for the auxiliary thoroughfare 5.

.It-shouldbe noted that the relay 61, associated withthe programtontroller M, is slow acting and does .not drop :out when the oontactors '49, 5| and 53 of the relay 3 associated with the time-delay sectors are in motion.

In the system of iEig. '1, therefore, the main thoroughfare keeps the go signal until a car stops on the auxiliary thoroughfare in front of .the street device for the time period required for the initiating sector 21 to move into contact with its fbrush 25 anditheJpredetermined period :required for :the timing sector :91 to revolve through the angle .in which it is in engagement with its brush II 'UI. After this time period, the stopsignal is given the .main thoroughfare for a predetermined time. The auxiliary thoroughfare remains 0pen,.and.cars may pass thereon, throughout the period of time last-mentioned; thereafter it remains cut-off until a car has stood before the street device thereon for the period mentioned above; and :the above-described cycle of signals is :repeated.

In systems of the type illustrated in Fig. l, the time-delay .is to a certain extent variable. Furthermore, provisions are not made in systems of this type for taking care of the density of traffic along the minor thoroughfare. Although automatic tralfic control systems wherein these two features are omitted :are highly useful in many localities, there are certain regions Where- :in it .ishighlydesira'ble that the two character- -isticsdiscussed above shall .be included.

In systems of the type illustrated in Fig. 2, these characteristics are included.

In apparatus of this type, the traffic signals .1 .are normally in the same condition as the signals in systems of the type illustrated in Fig. l. That is to say, under ordinary circumstances a go signal :is indicated for the main highway 3 :and-a stop-signal is indicated .for the auxiliary highway I.

Inthis case a plurality of bus lines IM and I09 leading .to a source of alternating current are provided. The lines are connected througha rectifying system Ix-I-I to a plurality of "bus lines H5 and H5 which supply direct current to the system. fWhenthe system is adjusted for traffic along the majorhighway 3, the time-delay motor III, which is in the present case asynchronous motor, .is connected to the direct current supply source and :the program control motor II=9, also a synchronous motor, is on open circuit. .Both of the motors I I1 and I I9 are therefore at rest.

The initiating sector 21 is in contact with its "brush .25 and the conducting segment 51 of the program control system is also in contact with its brushes 105.

When :a vehicle appears on the auxiliary highway:5 in such a position as to obstruct the light from the source 9 to'the photo-sensitiveelement "II, of one of the street devices, the exciting coil 5l 2 or I23 of a relay I25 or I21 associated therewith is 'deenergized. The relays I25.and I21 associated Withthe'street devices are each equipped with a single normally closed contactor 1:29 or I:3I and two normally'open oontactors 13.3 and I35, or 131 and I33.

In the following discussion it will be assumed I 25 is disturbed and hence the relay I25 deenergized.

When the relay 12 5 is deenergized, the closed. contactor I29 thereof "is opened, .a circuit from one direct current'bus'line -I I3 through a lead MI, vabranch lead .143, the exciting coil I of a relay :IA-I, (whereby the power applied .to the windings of the motor I I! which drives the time-delay device is changed'from alternating current to direct current), a lead I49, the closed contactor I3I of the relay I21, associated with the inactive street device, a lead I5I ,ithe closed contactor'll29 associated with the active street device, a lead I53, the initiating sector 2JI, the shaft 95, through which the initiating sector 21 and the timing sector 91 :are driven, a contacting'sector I and a lead I51 "that the street device associated with the relay 7 to the remaining direct current bus line II 5, is broken. When the relay I51 associated with the motor I I1 of the time-delay device is deenergized its core I59 drops, the circuit, through the contactor ISI, whereby direct current is supplied to the motor H1 is opened, and the circuit, through the contactor I63, whereby alternating current is supplied to the motor is closed. The motor II1 therefore begins to rotate.

Furthermore, the contactor I33 of the relay I25 associated with the active street device is closed by the obstruction of the light from the source 9 and as a result a circuit from one bus line IE3 through a lead I65, the exciting coil I51 of a relay I99, associated with the delay device, a lead IN, the newly closed contactor I33 of the street device relay I25, a lead I13, the lead I53, the initiating sector H, the contacting sector I55 and the lead I51 to remaining bus line I I5, is closed. The relay I69 is therefore energized and its lower normally closed contactor I is opened while its two upper contactors I11 and I19 which are normally open, are closed.

One of the latter contactors I19 shunts the initiating sector 2|, and as a result, provides a path for the current when the latter has passed out of engagement with its associated brush 25.

By the opening of the contactor I15, that is normally closed, a circuit from one bus line II 3, through a lead IBI, the coil I83 of a relay I85 associated with the program control system, a lead I81, the conducting sector 51 incorporated in this system, a lead I99, a branch lead I9I, the newly open contactor I15 of the relay I59 associated with the time-delay system, and a lead I93, to the remaining bus line I I5, is opened.

However, this circuit is not completely broken since it is closed by the remaining contactor I11 that is now closed. The new circuit is similar to the circuit discussed hereinabove in that it includes the exciting coil I83 of the relay I85 associated with the program control system and the conducting sector 51, incorporated in this system, but it also includes the timing sector 91, the shaft 95 whereon the timing sector 91 is mounted, the contacting sector I55, and the lead I51.

It is seen that the system is now transferred to a condition wherein its future history is determined by the timing sector 91. When the latter becomes disengaged from its brush I9 I, the relay I85 associated with the program controller I95 is deenergized and its core I94 drops, opening a circuit through the coil I83, whereby braking is removed from the motor H9 and closing the circuit through the motor. It is to be noted that the circuit through the motor passes from one alternating current bus line I91, through a lead I94, the closed contactor I95 of a relay I91, a branch lead I99, a lead 29 I the newly closed contactor 293 of the program control relay I85, the program control motor H9 and a lead 291 to the remaining alternating current bus line I09.

By reason of the rotation of the motor I I9, the program controller BI is rotated and the signals 1 pass through the predetermined cycle. However, an additional sector 299 is disposed on the motor shaft I63 and is rotated thereby. The sector 209 makes contact with a plurality of brushes 2I I as long as the right-of-way signal is indicated along the auxiliary highway 5. Hence, when the vehicle which caused the change in the traflic lights moves away from the position where it disturbed the active street device and a second vehicle approaches and causes the relay I associated with the street device to become deenergized, and the contactors I33 and I35 to close. and contactor I29 to open, the circuits to which reference was made hereinabove are effected to a certain degree, but, in addition, a circuit which was not mentioned heretofore and which is associated with the contactor I35 of the relay I25 and with the sector 299 is now also affected.

The new circuit from one bus line II3 of the direct-current source, through a lead 2 I2, the bimetal and heating coil of time-delay switch 2 I3, the lead 2M, the coil 2I5 of the relay I91, a lead 2I1, the sector 299, a lead 2I9, the contactor I39 of a street-device relay I21 and a lead 22I, to the remaining bus line II5 of the direct-current source, is closed. The trafiic-density relay I91 is therefore energized and a circuit from the directcurrent bus line I I 3 through a lead 223, the newly closed contactor 225, of the trafiic-density relay, the lead 5-29I the closed contactor 293 of the pro gram control relay I 85, the lead 295, motor H9, and the lead 251, to the remaining direct current bus line I I5, is closed. At the same time the circuit, through the contactor I95, whereby alternating current is supplied to the motor H9 is opened and as ,a result the motor is stopped. It is seen that as vehicles moving along the minor highway 5 pass through the light beam, the trafiic signalling system is delayed for an instant and tends to remain in a condition whereby it indicates a right-of-way for the minor highway.

The time-delay switch 2I3 functions in emergencies; that is to say, when the sources 9 burn out or when a vehicle stalls on the minor highway in the path of the exciting light beam. Under such circumstances the program controller 6i rotates until a go signal is indicated for the auxiliary highway 5 and then stops since the relay I91 is energized. However, this situation continues only until the bimetal of the time-delay switch 2 I 9 is heated to such a point that it opens. The relay I91 is then deenergized and the signal system is actuated from the program controller.

The mode of operation, under various trafiic conditions of Fig. 2, may be described as follows: Normally the main thoroughfare has the go signal until a car has stood in front of the street device on the auxiliary thoroughfare for a sufficient interval of time to initiate operation of the signal control motors. It is to be noted that the coil I53 of the relay I85 is maintained energized through the movable contactor I15 of relay I59 as long as there is no vehicle on the minor lane 5. When there is a vehicle on the minor lane the relay I85 is maintained energized through the movable contactor I11 of relay I89 and through the conducting segment 91 as long as it is in engagement with the brush IGI. In either case the motor II9 is deenergized and a go signal is displayed for the major lane 3.

When the sector91 is disengaged from the brush I 9i the go signal is given to the auxiliary thoroughfare. If no other cars appear on the auxiliary thoroughfare the go signal remains on the latter for a period of time determined by the synchronous speed of the motor I I9. If additional cars appear during this period on the auxiliary thoroughfare each introduces a time delay equal'to the period it consumes in passing the street device. The net result is, therefore, that the synchronous motor H9 rotates only during such periods of time as there is no interception of the light ray of the street device; and the go signal remains on the cross street until the sum of the time periods intervening between successive vehicles passing the street device equals the time required for the synchronous motor H9 to rotate the signal control contactor to the position at which the signal 1' changes. In other words, the signals change after the sum of the times, during which the light beam of the street device is uninterrupted, equals a predetermined period. Thereupon the go signal is given'to the main thoroughfare, and remains there until a vehicle has stood in front of the street device on the auxiliary thoroughfare for the time required to reinitiate action of the signal control; (1. e., until the sector 9'! again disengages the brush I01), whereupon the above-described cycle is repeated.

My invention has herein been illustrated as specifically applied to a system wherein a photosensitive system is utilized for a street device. 'It is apparent that a system of this type has certain advantages which do not apply to systems wherein, for example, the street device is of the acoustic, electromagnetic, electrostatic, or mechanical type. It will furthermore be recognized that the time delay device incorporated in my novel 7 system is particularly useful in connection with apparatus wherein the street device is of a photosensitive type. However, it should also be recognized that my invention may be utilized in connection with automatic traffic control systems wherein the street device is of the other types to which reference was made hereinabove.

In essence my invention comprises a trafiic control system wherein either a variable or a consive device which may be applied with simplicity.

As illustrated in the drawings, and as described above, the direct current for my system is derived from an alternating current supply source. It is apparent that the direct current may be supplied in any desirable manner, such, for example, as by independent batteries.

Finally it will be noted that the switches and the fuses which are ordinarily incorporated in trafiic control systems are not incorporated in the above material. The disposition of these' devices was deemed apparent, and hence it was felt that the drawings need not be unnecessarily complicated by their inclusion.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. Apparatus for controlling the movement of traffic along a plurality of highways comprising stop and go signals to be displayed for said highways, means including a moving element for determining by its average speed the time intervals between changes of said signals, a street device actuated only while a vehicle is opposite it, said street device being actuated by the first vehicle moving along one of said highways after a stop signal has been displayed thereon for initiating predetermined movement of said element during at least a part of which a go signal is displayed tothe last-mentioned highway, and means for thereupon rearrangingthe functional relations between said street device and said element to stop the movement of said element during such times as succeeding vehicles on the highway lastmentioned are so. positioned as to influence said street device as aforesaid and during the display of said go signal.

2. Apparatus for controlling traffic along a plurality of highways comprising stop and go signals to be displayed for said highways, a go signal being displayed for one of said highways and a stop signal for another of said highways, means for varying the display of said signals, trafiic-actuated means of a type that operates to provide a single actuating impulse whose length is dependent upon the time the vehicle is opposite to it, one said impulse to be impressed on said varying means for each vehicle actuating said actuated means, the length of said impulse being proportional to the, aggregate time a vehicle is 3. Apparatus for controlling the movement of trafiic along a plurality of highways comprising stop and go signals to be displayed for said highways, means to be motivated for varying the display of said signals at a rate dependent on the speed of movement thereof, a synchronous motor for actuating saidvarying means, a circuit including said motor and an alternating current source, a circuit including said motor and a directcurrent source, means for closing the first-named circuit and opening the last-named circuit to motivate said varying means and traiiic-actuated means of the type that operates to provide only a single actuating impulse whose length is dependent upon the time the vehicle is opposite it to be impressed on said circuitvarying means for each vehicle actuating said actuating means for opening the first-named circuit and closing the last-named circuit responsive to and for the duration of impulses created by said trafiic-actuated means.

4. Apparatus for controlling the movement of traffic along a plurality of highways comprising stop and go signals to be displayed for said highways, means to be motivated for varying the display of said signals at a rate dependent on the speed of movement thereof, a synchronous motor for actuating said varying means, a circuit including said motor and an alternating current source, a circuit including said motor and a directcurrent source, means for closing the first-named circuit and opening the last-named circuit to motivate said varying means, and trafiic-actuated means of the type that operates to provide an actuating impulse for a definite time to be impressed on said circuit-varying means for each vehicle actuating saidactuating means for opening the first-named circuit and closing the lastnamed circuit responsive to and for a time determined by the duration of impulses created by said traffic-actuated means.

. RICHARD C. HITCHCOCK. 

